Baltimore Orioles build remarkable, sock-like hanging nests, woven together from slender fibers. The female weaves the nest, usually 3 to 4 inches deep, with a small opening, 2 to 3 inches wide, on top and a bulging bottom chamber, 3 to 4 inches across, where her eggs will rest. She anchors her nest high in a tree, first hanging long fibers over a small branch, then poking and darting her bill in and out to tangle the hank. While no knots are deliberately tied, soon the random poking has made knots and tangles, and the female brings more fibers to extend, close, and finally line the nest. Construction materials can include grass, strips of grapevine bark, wool, and horsehair, as well as artificial fibers such as cellophane, twine, or fishing line. Females often recycle fibers from an old nest to build a new one. Males occasionally bring nesting material, but don’t help with the weaving. Building the nest takes about a week, but windy or rainy weather may push this as long as 15 days. The nest is built in three stages: first, the female weaves an outer bowl of flexible fibers to provide support. Next, springy fibers are woven into an inner bowl, which maintains the bag-like shape of the nest. Finally, she adds a soft lining of downy fibers and feathers to cushion the eggs and young.

Nest Placement

TreeThe female chooses a nest site within the territory defended by her mate. She anchors the nest firmly to a fork in the slender upper branches of a tree. Baltimore Orioles often nest in American elms, but will build in other trees, especially maples and cottonwoods. The distinctive nest usually hangs below a branch, but is sometimes anchored along a vertical tree trunk.